Superimposed diffraction gratings for eyepieces

ABSTRACT

Embodiments of the present disclosure are directed to techniques for manufacturing an eyepiece (or eyepiece layer) by applying multiple, different diffraction gratings to a single side of an eyepiece substrate instead of applying different gratings to different sides (e.g., opposite surfaces) of the substrate. Embodiments are also directed to the eyepiece (or eyepiece layer) that is arranged to have multiple, different diffraction gratings on a single side of the eyepiece substrate. In some embodiments, two or more grating patterns are superimposed to create a combination pattern in a template (e.g., a master), which is then used to apply the combination pattern to a single side of the eyepiece substrate. In some embodiments, multiple layers of patterned material (e.g., with differing refraction indices) are applied to a single side of the substrate. In some examples, the combined grating patterns are orthogonal pupil expander and exit pupil expander grating patterns.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 62/768,672 entitled “SUPERIMPOSED DIFFRACTION GRATINGSFOR EYEPIECES” and filed on Nov. 16, 2018, which is incorporated byreference herein in its entirety.

BACKGROUND

In optical devices, light can be directed and/or manipulated to achievea desired effect. For example, in an optical device such as an eyepieceused in a virtual reality or augmented reality interface, visible lightcan be directed and/or manipulated to provide image data that isperceived by a user. Some optical devices have a design that isnecessarily complex to achieve a desired effect, and the manufacturingprocess for such devices may therefore require exacting standards.Accordingly, the manufacture of the devices can be expensive, timeconsuming, and/or vulnerable to the introduction of defects. As such,device manufacturers seek techniques to simplify the manufacturingprocess where possible.

SUMMARY

Embodiments of the present disclosure are generally directed totechniques for simplifying complex optical devices (also described aseyepieces) by applying multiple, different diffraction gratings to asingle side of an eyepiece substrate instead of applying differentgratings to different sides (e.g., opposite surfaces) of the substrate.More specifically, embodiments are directed to creating a template (alsodescribed as a master) by superimposing at least two different patternsto provide a combination pattern in the template, and using the templateto imprint the combination pattern onto the substrate of the eyepiece toachieve the desired optical properties of the eyepiece. Embodiments arealso directed to applying multiple layers of patterned material (e.g.,with differing refraction indices) to a single side of the substrate toachieve the desired optical properties.

In general, innovative aspects of the subject matter described in thisspecification can be included in one or more embodiments of a method forproviding a template that is usable for applying a grating pattern to awaveguide, the method including: forming a first pattern in a first sideof a template substrate; and forming a second pattern in the first sideof the template substrate to form the template, the second pattern beingsuperimposed onto the first pattern in the template substrate to formthe template that includes, on one side of the template, a combinedpattern that is a combination of the first pattern and the secondpattern, wherein the first pattern corresponds to one of an orthogonalpupil expander (OPE) grating or an exit pupil expander (EPE) grating,and wherein the second pattern corresponds to a different one of the OPEgrating or the EPE grating.

One or more embodiments can optionally include one or more of thefollowing features: forming the first pattern in the first side of thetemplate substrate includes etching the first pattern; forming thesecond pattern in the first side of the template substrate includesusing lithography to imprint the second pattern; forming the secondpattern in the first side of the template substrate includestransferring the second pattern from resist into the template substrateusing dry etching; the template substrate is composed at least partly ofone or more of SiO₂ and Si; the method further including employing thetemplate to apply the combined pattern to one side of the waveguide,such that the combined pattern on the waveguide exhibits both OPE andEPE diffraction properties; and/or employing the template furtherincludes contacting the template with a polymerizable material arrangedon the one side of a substrate of the waveguide, solidifying thepolymerizable material to form, on the one side of the substrate, thecombined pattern based on the template, and separating the template fromthe substrate. The refractive index of the OPE grating may exceed therefractive index of the EPE grating. The refractive index of thesubstrate may exceed the refractive index of the OPE grating and therefractive index of the EPE grating. A difference between the refractiveindex of the OPE grating and the refractive index of the EPE grating maybe at least 0.2. The OPE grating, the EPE grating, or both may include aline grating, pillars or holes, or both.

Innovative aspects of the subject matter described in this specificationcan also be included in one or more embodiments of a waveguide structurethat includes a substrate and a combined pattern applied to one side ofthe substrate, wherein the combined pattern is a superposition of anorthogonal pupil expander (OPE) diffraction grating pattern and an exitpupil expander (EPE) diffraction grating pattern, such that the combinedpattern on the waveguide structure exhibits both OPE and EPE diffractionproperties.

One or more embodiments can optionally include one or more of thefollowing features: the waveguide structure further includes anin-coupling grating (ICG) pattern; and/or the substrate is glass. Therefractive index of the OPE diffraction grating pattern may exceed therefractive index of the EPE diffraction grating pattern. The refractiveindex of the substrate may exceed the refractive index of the OPEdiffraction grating pattern and the refractive index of the EPEdiffraction grating pattern. A difference between the refractive indexof the OPE diffraction grating pattern and the refractive index of theEPE diffraction grating pattern may be at least 0.2. The OPE diffractiongrating pattern, the EPE diffraction grating pattern, or both mayinclude a line grating, pillars or holes, or both.

It is appreciated that aspects and features in accordance with thepresent disclosure can include any combination of the aspects andfeatures described herein. That is, aspects and features in accordancewith the present disclosure are not limited to the combinations ofaspects and features specifically described herein, but also include anycombination of the aspects and features provided.

The details of one or more embodiments of the present disclosure are setforth in the accompanying drawings and the description below. Otherfeatures and advantages of the present disclosure will be apparent fromthe description and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 depicts a schematic of an example eyepiece of a previouslyavailable configuration.

FIG. 2 depicts a schematic of an example eyepiece, according toembodiments of the present disclosure.

FIG. 3 depicts an example process for creating a template to apply acombination grating pattern to an eyepiece, according to embodiments ofthe present disclosure.

FIGS. 4A and 4B show images of a template created according toembodiments of the present disclosure.

FIGS. 5A-5D show images of combination pattern imprinted onto aneyepiece, according to embodiments of the present disclosure.

FIG. 6 depicts a schematic of an example eyepiece, according toembodiments of the present disclosure.

FIGS. 7-10 depict example processes for applying multiple layers ofpatterns, according to embodiments of the present disclosure.

DETAILED DESCRIPTION

Embodiments of the present disclosure are directed to techniques formanufacturing an eyepiece (or a layer of an eyepiece) by applyingmultiple, different diffraction gratings to a single side of an eyepiecesubstrate instead of applying different gratings to different sides(e.g., opposite surfaces) of the substrate. Embodiments are alsodirected to the eyepiece (or eyepiece layer) that is arranged to havemultiple, different diffraction gratings on a single side of theeyepiece substrate.

In some embodiments, two or more grating patterns are superimposed tocreate a combination pattern in a template (e.g., a master), which isthen used to apply the combination pattern to a single side of theeyepiece substrate. In some embodiments, multiple layers of patternedmaterial (e.g., with differing refraction indices) are applied to asingle side of the substrate. For example, an eyepiece utilizing a highindex glass diffraction grating waveguide is formed as a compositestructure of (e.g., silicone-acrylate) adhesive, inorganicanti-reflective coating, high-index glass substrate, and patternedpolymer gratings.

Embodiments provide a diffraction grating based waveguide display thatcan be used for a near-eye display, such as in a virtual reality oraugmented reality apparatus. Some embodiments employ a 3D patternoverlaid architecture in the final waveguide architecture or use it toetch a modified 3D pattern into templates, which can then be used toimprint nano-structures on transparent substrates to make near-eyedisplay eyepiece. The 3D overlaid pattern in the imprinted device and/ortemplate combine multiple, different diffraction gratings into one 3Dpattern. Accordingly, embodiments enable the avoidance of multi-imprints(e.g., a double-sided imprint as described below) and instead providefor a single imprint with similar planform area.

Traditionally, an eyepiece can include various eyepiece grating regionswith different refraction gratings to achieve various optical effects.Such regions can include an orthogonal pupil expander (OPE) region, anexit pupil expander (EPE) region, and an in-coupling grating (ICG)region. When the eyepiece is included as a component of a virtualreality headset, augmented reality headset, or other suitable apparatus,a projector of the apparatus may project image light onto the ICG regionof an eyepiece layer. The ICG region can couple the image light from theprojector into a planar waveguide that propagates the light in adirection toward the OPE region. The waveguide may propagate the imagelight in the horizontal direction through internal reflection. The OPEregion can include a diffractive grating that multiplies and redirects aportion of the image light toward the EPE region. For example, the OPEregion may multiply the light in an orthogonal direction within thewaveguide and direct the multiplied light to various portions of the EPEregion. The EPE region can include a (e.g., different) diffractivegrating that out-couples and directs at least a portion of the light, ina direction outward from the plane of the eyepiece layer, and/or towardthe human viewer's eye. For example, the EPE grating can direct light atan angle that is substantially perpendicular to the plane of theeyepiece layer, and/or at some other angle such as a 45 degree anglerelative to the plane of the eyepiece layer depending on specific designcharacteristics of the grating dimensions. In this fashion, an imageprojected by the projector may be received and viewed by the viewer'seye.

For mixed reality (e.g., augmented or virtual reality) diffractiongrating waveguide displays, EPE and OPE regions have been traditionallyused to display an image with an expanded pupil area. In some previouslyavailable solutions, OPE and EPE regions were arranged in differentportions of the eyepiece. Later, to reduce form factor area, EPE and OPEregions were imprinted on the opposite sides of the transparentsubstrate. An example of such double-side imprinting is shown in FIG. 1.FIG. 1 shows an example of double-side imprinting of an eyepiece 102. Ineyepiece 102, the EPE region 106 and the OPE region 108 are arranged onopposite sides of the substrate 104, in an area of the eyepiece 102that, for example, may be separate from the ICG region 110.

This double-side imprinting typically requires strict angle alignmentbetween the two sides, and also typically requires both sides of thesubstrate to be clean. Such constraints can make the double-sideimprinting process more complicated, e.g., by reducing speed andthroughput of the manufacturing, increasing cost, and providing anincreased likelihood of the introduction of manufacturing flaws.Moreover, the double-sided imprinting prevents the use of ananti-reflective coating or other application on both sides of thesubstrate, where the use of such an application may otherwise provideadvantages.

FIG. 2 depicts a schematic of an example eyepiece 202, according toembodiments of the present disclosure. In this example, the OPE and EPEregions are combined into a combination grating 204 that is imprintedonto one side of the substrate 104. For example, a template 206 (e.g., amaster) can be created to includes a superposition of (e.g., inverse ornon-inverse versions of) the OPE and EPE gratings, and the template canbe used to imprint the combination grating 204 as a 3D structure onto asingle side of the eyepiece 202.

FIG. 3 depicts an example process for creating the template 206, whichcan be employed to imprint the combination OPE and EPE pattern 204 ontoany suitable number of eyepieces. In this example, a 3D template isfabricated using a double etch method.

During a first phase 302, the first (e.g., OPE) pattern is etched on thetemplate, to generate a partially etched template 304, which is alsoshown in perspective view 306. The template substrate can be anysuitable material, such as SiO₂, Si, and so forth. This example showsthe first grating pattern as a circle hole 2D grating, but other shapesor patterns can also be used such as a square pattern, pillar tone, andso forth. The grating array is shown as square, can also be some otherarray such as a diamond array.

During a second phase 308, the second (e.g., EPE) pattern is imprintedor otherwise formed on top of the template 304 to generate the template310, which is also shown in perspective view 312. The second pattern canbe a one- or two-dimensional pattern and can include line gratings,pillars, holes, or any known diffraction pattern designed to modify anangle of propagation of light such that it exits the waveguide. Theimprinting of the second pattern can be through lithography, such as anysuitable technique for imprint lithography, photo-lithography, e-beamlithography, and so forth. This phase can apply patterned resist for thesecond pattern on top of the etched first pattern. In some examples, thesecond pattern is transferred from resist into substrate using dry etch,and/or the resist is striped after the dry etching, to combine the twopatterns into one 3D pattern. In some examples, the OPE pattern isapplied first (e.g., in the first phase), and the EPE pattern is appliedon top (e.g., in the second phase). Alternatively, the EPE pattern canbe applied first, followed by the OPE pattern. In either example, thecompleted 3D template can be used to apply the combination pattern tothe eyepiece which has both the OPE and EPE diffraction properties.

FIG. 4A is a perspective cross-sectional view of template 400 createdaccording to embodiments of the present disclosure. FIG. 4B is a topview of template 410, which includes line grating 412 and holes 414.

FIG. 5A is an image of the combination pattern imprinted onto aneyepiece, according to embodiments of the present disclosure. As shown,a single waveguide 500 can include multiple regions or zones havingdifferent grating structures. For example, a first zone 502 can includeincoupling gratings (ICGs), such as line gratings, configured to receiveinput light from a projector and alter the propagation angles such thatthe light can move through the waveguide by total internal reflectiontoward a second zone. The second zone 504 can include different gratingstructures than the first zone 502. As shown, the second zone 504 caninclude at least one of an OPE or an EPE structure. FIG. 5B shows linegratings 510 in first zone 502. FIG. 5C shows second zone 504 with a 2Dgrating having pillars or holes 512, to divide and redirect at least aportion of the light to spread and multiply the image light within theplane of the waveguide and toward a third zone 506. The third zone 506can include a combined OPE/EPE grating structure as described hereinwith respect to FIG. 3, for example. FIG. 5D shows line grating 520 andholes 512 in third zone 506. One of skill in the art will appreciatethat other configurations are possible, the configurations having moreor fewer zones of different diffraction grating structures. For examplea waveguide can have a zone with ICG grating structures directing lightdirectly to a zone having a combined single-sided OPE/EPE gratingstructure, such as a single-sided 3D grating structure. Each zone canhave grating structures formed on top of or within the waveguidematerial.

The examples of FIGS. 4 and 5 show an opposite pattern tone. The imprintlithography process can involve a single tone reversal in which thetemplate and final imprint on the substrate are of opposite tones.Alternatively, the imprint lithography process can involve a two tonereversal in which an intermediate template is made from the oppositetone of the template and the template's tone is transferred as is to thefinal substrate (e.g., with the opposite tone of the intermediatetemplate). The intermediate template can be an imprint lithography basedtemplate of rigid or flexible substrate that is made using additionalprocessing steps such as CVD, PVD, and/or plasma based processes.

The combination pattern that is a superposition of the OPE and EPEpatterns can be described as a first architecture for the eyepiecegratings. Embodiments also support a second architecture of combiningthe OPE and EPE patterns on the same side of a (e.g., high refractiveindex) substrate. This second architecture can include a relief layerstructure EPE patterned over OPE both using a different index material.The first pattern can either be etched into the substrate surface orcoating over a surface to form a first set of relief structures. Thesecond set of relief structures can be patterned over the first set,with a different index material, thus arranging the first relief layerunder the second set of relief structures.

FIG. 6 shows an example eyepiece 602 arranged per one example of thissecond architecture. As shown in this example, the first pattern 604(e.g., OPE) is applied to one side of the substrate 104, and the secondpattern 606 (e.g., EPE) is applied on top of the first pattern 604. Thelight coming to the first OPE layer through internal reflection iscoupled out toward the EPE structure sitting over the OPE layer. The OPElayer also sends a portion of that light orthogonally towards otherareas of the OPE which then further couple light out through the EPEthus spreading the light as intended by the OPE structure.

In examples of the second architecture, the OPE and EPE reliefstructures can be packed vertically and very close on one side of thesubstrate. This, in such embodiments, instead of arranging OPE and EPEpatterns on opposite surfaces of a flat thick (e.g., 300 μm) substrateas in previously available solutions, the OPE and EPE patterns caninstead be separated by a distance of several hundred nanometers.

Both architectures enable OPE and EPE functionality to be combinedeither with material of one index or varying the index of the two layerssandwiched together. This enables imprinting both structures on oneside, making manufacture simpler, faster, and higher quality, whilestill retaining the benefits of a wide field of view provided by thepreviously available overlap design. By applying the patterns on oneside, both architectures leave the oppose side available for some othertype of treatment, such as the application of an anti-reflectivecoating, the application of a laminate or epoxy to affix cover glass tothe opposite side, and so forth. For both architectures, the applicationof patterns to one side can provide greater efficiency, lower cost,and/or fewer defects during manufacture. For example, application on oneside may remove the need to flip the substrate during manufacture toapply a grating to the opposite side, as in previously availabletechniques. Application to one side also can reduce or eliminateproblems with misalignment of the OPE and EPE layers. In the firstarchitecture, the alignment can be imposed during the creation of thetemplate, and alignment may be more reliable given the application ofthe two gratings to the same side of the template to create thecombination pattern. In the second architecture, applying multiplelayers on one side makes it easier to ensure more accurate alignment ofthe OPE and EPE layers because there is not a step of flipping thesubstrate between the application of the OPE and EPE gratings, as inpreviously available techniques.

In various embodiments for the second architecture, the OPE structure(grating) may be situated substantially between the EPE structure andthe substrate. The OPE structure may be made of a material that has adifferent refractive index from the material that is used for the EPEstructure. In one example, the OPE structure may have a refractive indexof 1.65, and the EPE structure may have a refractive index of 1.52, withthe substrate having a refractive index of 1.8. In some embodiments, therange of refractive indices of the employed materials for each layer mayvary from 1.3 to 3.0, and embodiments may employ materials in which adifference between the refractive indices of the two layers (OPE andEPE) is at least 0.2. For example, the difference may be 0.25. Thematerials used may be adjusted to achieve a difference in refractiveindex that provides a desired brightness, contrast, and/or otherproperties of the image.

FIGS. 7-10 depict example processes for applying multiple layers ofpatterns to one side of a substrate, according to embodiments of thepresent disclosure.

As shown in the example of FIG. 7, during a first phase 702 a substance706 with a first refractive index (e.g., 1.65) is applied to one side ofthe substrate 708, and a first template 704 is used to mold thesubstance 706 into the pattern 710 for the OPE layer. During a secondphase 712, a substance 716 with a second, lower refractive index (e.g.,1.52) is applied on top of the OPE pattern 710, and a second template714 is used to mold the substance 716 into the pattern 718 for the EPElayer. First and second substances 706 and 716 can be cured to formfirst and second patterns 710 and 718, respectively, using methods suchas UV curing and/or thermal curing as determined by their respectivechemical compositions.

As shown in the example of FIG. 8, during a first phase 802 a substance806 with a first refractive index is applied to one side of thesubstrate 808, and a first template 804 is used to mold the substance806 into the pattern 810 for the OPE layer. During a second phase 812, asecond material 814 is deposited on top of the OPE layer. The secondmaterial 814 can have a higher index of refraction (e.g., 3 or higher)than the first material 806. The deposition of the second material 814may be through any suitable technique, including physical vapordeposition (PVD) (e.g., sputter and evaporation), chemical vapordeposition (CVD) (e.g., atmospheric pressure plasma enhanced CVD(APPECVD), atomic layer deposition (ALD), low pressure plasma enhancedCVD (LPPECVD), etc.), and so forth. During a third phase 816, asubstance 820 is applied on top of the layer of second material 814, anda second template 818 can be used to mold the substance 820 into thepattern 822 for the EPE layer. The third substance 820 may have asimilar or same refractive index as the first material 806, and/or lowerthan the refractive index of the high index material 814.

As shown in the example of FIG. 9, during a first phase 902, a lowerindex material 904 can be patterned over a higher index coating 906 onthe substrate 908 as described above with reference to FIGS. 7 and 8.During a second phase 910, the higher index coating 906 can be etched toprovide the OPE layer 912. During a third phase 914, the lower indexmaterial 904 is patterned over the higher index pattern 912, to providethe EPE layer 916.

The technique of FIG. 9 can be modified somewhat, such that the lowerindex substance is patterned directly onto the substrate (which has ahigher index), without using the intermediary higher index coating 906.FIG. 10 shows an example of this technique. During a first phase 1002, alower index material 1004 can be patterned over the higher indexsubstrate 1006. During a second phase 1008, the higher index substrate1006 can be etched to provide the OPE layer 1010. During a third phase1012, the lower index material 1004 is patterned over the higher indexpattern 1010, to provide the EPE layer 1014.

Implementations support various suitable structures and geometries ofthe patterns that may be applied to the substrate. For example, thepatterns can be a symmetric stepped, tapered structure, or an asymmetric(e.g., blaze) structure such as a saw-tooth, slanted, and/or multi-steppattern of features.

The eyepiece may have any suitable number of layers of glass or othermaterial, and each layer may act as a waveguide to allow the passage ofvarious frequencies of light. For a single layer eyepiece, the gratingapplication techniques described herein may be used to apply gratings toone side of the eyepiece. For a multi-layer eyepiece, the gratingapplication techniques described herein may be used to apply gratings toone side of at least one of the layers. In some examples, layers may beconfigured as waveguides for particular wavelengths, so as to propagatelight of a particular color, and the eyepiece may be configured for aparticular optical power, to create a number of depth planes at whichlight through the waveguide may be perceived. For example, a first setof waveguide layers may include layers for red, green, and blue light ata first depth plane, and a second set of waveguide layers may include asecond set of layers for red, green, and blue light corresponding to asecond depth plane. The order of the colors may be arranged differentlyin different depth planes to achieve the desired optical effects in theeyepiece. In some embodiments, a single (e.g., blue) layer may covermultiple depth planes.

In some examples, the eyepiece may be created at least in part using Jetand Flash Imprint Technology (J-FIL™), developed by Molecular Imprints™.The J-FIL technique may be used to create diffraction gratings on thelayers of the glass of the eyepiece to create waveguide displays. Eachlayer may be a thin layer of glass with polymer gratings created on itssurface using J-FIL. The diffraction gratings may provide the basicworking functionality of the layer, and multiple layers may be stackedto assemble the eyepiece. Once the diffraction gratings are formed ontoa large, broad glass layer, the glass layer may be laser cut into theshape of the eyepiece. Each layer of glass may be a different color, andthere may be multiple depth planes. A larger number of planes mayprovide for a better virtual experience for a user using the eyepiece.The layers may be stacked using the sealant polymer (e.g., glue dots orline), and the whole stack may be sealed using a sealant in someexamples, to provide structural integrity, preserve a gap betweenlayers, prevent contamination, and/or prevent back-reflection of lightwithin the eyepiece.

While this specification contains many specific details, these shouldnot be construed as limitations on the scope of the disclosure or ofwhat may be claimed, but rather as examples of features that areassociated with particular embodiments. Certain features that aredescribed in this specification in the context of separate embodimentsmay also be implemented in combination in a single embodiment.Conversely, various features that are described in the context of asingle embodiment may also be implemented in multiple embodimentsseparately or in any suitable sub-combination. Moreover, althoughfeatures may be described above as acting in certain combinations andeven initially claimed as such, one or more features from a claimedcombination may in some examples be excised from the combination, andthe claimed combination may be directed to a sub-combination orvariation of a sub-combination.

A number of embodiments have been described. Nevertheless, it will beunderstood that various modifications may be made without departing fromthe spirit and scope of the disclosure. For example, various structuresshown above may be used, with elements rearranged, positioneddifferently, oriented differently, added, and/or removed. Accordingly,other embodiments are within the scope of the following claims.

What is claimed is:
 1. A method of making a template for applying agrating pattern to a waveguide, the method comprising: forming a firstpattern in a first side of a template substrate; and forming a secondpattern in the first side of the template substrate to form thetemplate, the second pattern being superimposed onto the first patternin the template substrate to form the template that includes, on oneside of the template, a combined pattern that is a combination of thefirst pattern and the second pattern, wherein the first patterncorresponds to one of an orthogonal pupil expander (OPE) grating or anexit pupil expander (EPE) grating, and the second pattern corresponds toa different one of the OPE grating or the EPE grating.
 2. The method ofclaim 1, wherein forming the first pattern in the first side of thetemplate substrate includes etching the first pattern.
 3. The method ofclaim 1, wherein forming the second pattern in the first side of thetemplate substrate includes imprinting the second pattern.
 4. The methodof claim 1, wherein forming the second pattern in the first side of thetemplate substrate includes transferring the second pattern from resistinto the template substrate using dry etching.
 5. The method of claim 1,wherein the template substrate is composed at least partly of one ormore of SiO₂ and Si.
 6. The method of claim 1, further comprising:employing the template to apply the combined pattern to one side of thewaveguide, such that the combined pattern on the waveguide exhibits bothOPE and EPE diffraction properties.
 7. The method of claim 6, whereinemploying the template further comprises: contacting the template with apolymerizable material arranged on the one side of a substrate of thewaveguide; solidifying the polymerizable material to form, on the oneside of the substrate, the combined pattern based on the template; andseparating the template from the substrate.
 8. The method of claim 1,wherein the refractive index of the OPE grating exceeds the refractiveindex of the EPE grating.
 9. The method of claim 8, wherein therefractive index of the template substrate exceeds the refractive indexof the OPE grating and the refractive index of the EPE grating.
 10. Themethod of claim 8, wherein a difference between the refractive index ofthe OPE grating and the refractive index of the EPE grating is at least0.2.
 11. The method of claim 8, wherein the OPE grating, the EPEgrating, or both comprise a line grating.
 12. The method of claim 8,wherein the OPE grating, the EPE grating, or both comprise pillars orholes.
 13. A waveguide structure, comprising: a substrate; and acombined pattern applied to one side of the substrate, wherein thecombined pattern is a superposition of an orthogonal pupil expander(OPE) diffraction grating pattern and an exit pupil expander (EPE)diffraction grating pattern, such that the combined pattern on thewaveguide structure exhibits both OPE and EPE diffraction properties.14. The waveguide structure of claim 13, further comprising anin-coupling grating (ICG) pattern.
 15. The waveguide structure of claim13, wherein the substrate is glass.
 16. The waveguide structure of claim13, wherein the refractive index of the OPE diffraction grating patternexceeds the refractive index of the EPE diffraction grating pattern. 17.The waveguide structure of claim 13, wherein the refractive index of thesubstrate exceeds the refractive index of the OPE diffraction gratingpattern and the refractive index of the EPE diffraction grating pattern.18. The waveguide structure of claim 13, wherein a difference betweenthe refractive index of the OPE diffraction grating pattern and therefractive index of the EPE diffraction grating pattern is at least 0.2.19. The waveguide structure of claim 13, wherein the OPE diffractiongrating pattern, the EPE diffraction grating pattern, or both comprise aline grating.
 20. The waveguide structure of claim 13, wherein the OPEdiffraction grating pattern, the EPE diffraction grating pattern, orboth comprise pillars or holes.